## Measurement and Uncertainty

Apparatus:

Vernier callipers, micrometer, sheet showing how to use the vernier and micrometer, 30cm ruler,

5 x 2p coins, set-square, top-pan balance (shared with the rest of the group).

Procedure:

1. Use the 30cm ruler to measure the diameter ONCE of one of your 2p coins.

Make an estimate of how uncertain you are of your value (eg a too large estimate would be ± 5mm) Your final answer should be expressed:

“The diameter of the 2p coin measured with the 30cm ruler was 56 ± 5mm”

NOTE: You only write the unit ‘mm’ once.

2. Now use the vernier callipers to measure the diameter ONCE of the same 2p coin.

Again make an estimate of how uncertain you are of your value (eg a too large estimate would be ± 0.9 mm) Your final answer should be expressed:

“The diameter of the 2p coin measured with the vernier callipers was 56.7 ± 0.9 mm”.

Now place all your five coins in a row and use the ruler to measure distance 5D as shown in the diagram below. You should find a way of making use of the set-square here.

3. From your reading obtain another value for the diameter and an uncertainty.

Your final answer should be expressed:

“The average diameter of one of five 2p coins measured along a line with a ruler was...

4. (a) Which of the above measurements of the diameter of a 2p is best?

(b) Explain your choice.

(c) Explain how taking more measurements in stages 1 & 2 would help.

5. Use the best methods possible to obtain a value for the:

(a) thickness of a 2p coin

(b) mass of a 2p coin.

6. Calculate the density of the coin.

7. Explain how you obtained your measurements for the thickness and mass.

8. Estimate the uncertainty in your density value.